The hydraulis is a predecessor of which modern instrument

The hydraulis is a predecessor of a church organ. (modern church organ)

Explanation:

Hydraulis, is earliest known mechanical pipe organ. It was invented by Ctesibius of Alexandria, an engineer in 3rd century BC. The hydraulis is a water driven pipe (instrument) and was the world's first keyboard instrument. It was the predecessor of the modern church organ.

The hydraulis has a reservoir of air which is inserted into a cistern of water. The air is pushed into the reservoir with hand pumps, and exits the reservoir as pressurized air to blow through the pipes.

These organs in churches, cathedrals or halls are very large in size, and are built especially for the these specific buildings.They are called “pipe organs” to distinguish them from modern “electronic organs”.

the previous answer given.